1. Field of the Invention
The present invention relates in general to a wireless relay of a wireless communication system and, more particularly, to a method and apparatus for designing backhaul sub-frames of an uplink and a downlink for a layer-3 relay including the functions of a base station.
2. Description of the Related Art
In modern mobile communication systems, Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier Frequency Division Multiple Access (SC-FDMA) have been widely studied as useful techniques for high-rate data transmission in a wireless channel. OFDM and SC-FDMA techniques are employed respectively for the downlink and uplink standardized by the Evolved UMTS Terrestrial Radio Access (E-UTRA) based on the third Generation Partnership Project (3GPP) Universal Mobile Telecommunication Services (UMTS) technology. SC-FDMA is a technique based on single carrier transmission while allowing the orthogonality of a multi-user like OFDM. The primary advantage of SC-FDMA is a lower Peak-to-Average Power Ratio (PAPR) of a transmission signal. Therefore, the SC-FDMA technique applied to mobile communication systems may enhance the cell coverage because of its lower PAPR in comparison with the OFDM technique.
A Long Term Evolution Advanced (LTE-A) system allows a higher rate data transmission than a conventional LTE system, thus requiring a new technique for compensating signal distortion. Normally signal distortion due to a path loss of a channel is one of critical restrictions in high-rate data transmission under limited resources. A wireless relay technique is introduced to overcome the above problem. In this technique, a wireless relay node disposed between an initial transmitter and a final receiver compensates a path loss of a signal delivered from the transmitter and sends a compensated signal to the receiver. That is, such a wireless relay technique improves a path loss unfavorably occurring between the transmitter and the receiver, thus allowing the improvement in performance of user equipment at cell peripheries and the extension of system coverage.
If a wireless relay node simultaneously performs signal reception and transmission, a transmitted signal may often act as interference to a received signal. Thus, a wireless relay node requires a separation between a reception link and a transmission link. These links may be separated as shown in Table 1.
TABLE 1Time DivisionSeparation of Transmission/Reception Links inSchemeDifferent Time Resources at Same Frequency BandFrequencySeparation of Transmission/Reception Links inDivision SchemeDifferent Frequency Resources at Same TimeResource
In Table 1, the frequency division scheme may need a broad gap between adjacent frequency bands so as to avoid interference between such bands. Thus, the time division scheme is normally used for an effective allocation of frequency resources.
Additionally, as shown in Table 2, a wireless relay system may be classified into four types according to the function of a relay node.
TABLE 2Layer-0(L0)Amplify and Deliver All Received SignalsRelayLayer-1(L1)Amplify and Deliver Received SignalsRelayLayer-2(L2)Demodulate, Decode, Encode, Modulate andRelayDeliver Received SignalsLayer-3(L3)Perform Functions of Base Station Including RelayRelayFunction
Particularly, the L3 relay system may allow a distinction between a relay node cell and a macro cell, make better use of frequency resources, and facilitate the introduction of a wireless relay in a cellular system.
A dominant feature of the L3 relay system is a wireless backhaul link between a base station and a relay node. A wireless backhaul link means that a relay node receives downlink data of user equipment from a base station or transmits uplink data of user equipment to a base station. A relay node distinguishes such a backhaul link from links with user equipment according to the time division scheme.
A relay node should perform a Radio Frequency (RF) transmission/reception switching before and after a backhaul sub-frame. Unfortunately, this may cause a switching time delay at a relay node. Therefore, backhaul sub-frames of the uplink and downlink in the L3 relay system should be designed in consideration of a time delay in an RF transmission/reception switching and the compatibility with sub-frames of normal uplink and downlink.